The invention is directed to water-soluble, fiber-reactive dyestuff compositions and a process for using these compositions to dye polyamide fibers. The fiber-reactive, water-soluble dyestuffs useful in the practice of this invention are those of the vinyl-sulfone type which are well known. In the dyeing of a polyamide fiber, the vinyl sulfone group forms a chemical bond with the amino groups of the fiber which fixes the dye to the fiber by a strong covalent chemical bond.
The chemical bonding of the dye molecule to the fiber by means of the vinyl sulfone group has many advantages. However, the vinyl-sulfone reactive dyes have not gained acceptance in the dyeing of polyamide. This is because it is difficult to get well-penetrated, level, uniform dyeings especially with two or three color mixtures. The vinyl-sulfone type dyes tend to selectively concentrate on one portion of the fiber leaving other portions deficient in that color either due variations in the fiber's morphology or the strike rate of the dye or a combination of both. This problem is particularly evident in the dyeing of polyamide materials where the fiber is highly extended, for example, in nylon carpet or rug materials and where the dyeing is done by the continuous method.
In the art, a dyestuff's initial diffusion and reactivity properties are characterized as its "strike" rate and as used in this description it is intended to characterize the initial dyeing rate or uptake of a dye by a substrate in the early stages of the dyeing process. The stroke rates of reactive vinyl-sulfone type dyestuffs towards polyamide fibers makes them unacceptable for many commercial polyamide dyeing applications, both in exhaust and continuous dyeing procedures where the acid dyes are more commonplace. Acid dyestuffs, however, form a salt bond with the polyamide which is susceptible to breaking under the influence of moisture and heat which results in a loss or bleeding of the dye--i.e. reduced fastness.
The dyestuff compositions of this invention comprise the reaction product of vinyl-sulfone type reactive dyes with N-alkyl-amino-alkyl sulfonic and carboxylic acids or their salts, wherein mole ratio of the above secondary amine is about 0.5 to about 1 mole for each mole of vinyl-sulfone type dye. These compositions when applied to polyamides by the process of this invention at a pH value of 3 to 4 provide uniform, level, well-penetrated dyeings having superior fastness properties.
U.S. Pat. No. 3,802,837 teaches that the reaction product of 1.5 to 4 moles of N-methyltaurine per mole of vinyl-sulfone type dye has increase solubility and increased reactivity in the exhaust dyeing of wool at a pH of 5. We have found that vastly improved polyamide dyeings can be achieved at reduced material cost using the dyestuff compositions and process of this invention.